at the point pclose might receive and act on cancellation, it has
already invalidated the FILE passed to it. thus, per musl's QOI
guarantees about cancellation and resource allocation/deallocation,
it's not a candidate for cancellation.
if it were required to be a cancellation point by posix, we would have
to switch the order of deallocation, but somehow still close the pipe
in order to trigger the child process to exit. i looked into doing
this, but the logic gets ugly, and i'm not sure the semantics are
conformant, so i'd rather just leave it alone unless there's a need to
change it.
close was the only cancellation point called from popen, but it left
popen with major resource leaks if any call to close got cancelled.
the easiest, cheapest fix is just to use a non-cancellable close
function.
if the buffer is too short, at least return a partial string. this is
helpful if the caller is lazy and does not check for failure. care is
taken to avoid writing anything if the buffer length is zero, and to
always null-terminate when the buffer length is non-zero.
this one could never cause any problems unless the compiler/machine
goes to extra trouble to break oob pointer arithmetic, but it's best
to fix it anyway.
dynamic-allocation of the structure is not valid; it can crash an
application if malloc fails. since localeconv is not specified to have
failure conditions, the object needs to have static storage duration.
need to review whether all the values are right or not still..
if we eventually have build options, it might be nice to make an
option to dummy this out again, in case anybody needs a system-wide
disable for disk/ssd-thrashing, etc. that some daemons do when
logging...
large precision values could cause out-of-bounds pointer arithmetic in
computing the precision cutoff (used to avoid expensive long-precision
arithmetic when the result will be discarded). per the C standard,
this is undefined behavior. one would expect that it works anyway, and
in fact it did in most real-world cases, but it was randomly
(depending on aslr) crashing in i386 binaries running on x86_64
kernels. this is because linux puts the userspace stack near 4GB
(instead of near 3GB) when the kernel is 64-bit, leading to the
out-of-bounds pointer arithmetic overflowing past the end of address
space and giving a very low pointer value, which then compared lower
than a pointer it should have been higher than.
the new code rearranges the arithmetic so that no overflow can occur.
while this bug could crash printf with memory corruption, it's
unlikely to have security impact in real-world applications since the
ability to provide an extremely large field precision value under
attacker-control is required to trigger the bug.
for seekable files, posix imposed requirements on the offset of the
underlying open file description after a stream is closed. this was
correctly handled (as a side effect of the unconditional fflush call)
when streams were explicitly closed by fclose, but was not handled
correctly at program exit time, where fflush(0) was being used.
the weak symbol hackery is to pull in __stdio_exit if either of
__toread or __towrite is used, but avoid calling it twice so we don't
have to keep extra state. the new __stdio_exit is a streamlined fflush
variant that avoids performing any unnecessary operations and which
never unlocks the files or open file list, so we can be sure no other
threads write new data to a stream's buffer after it's already
flushed.
there is no need/use for a flush hook. the write function serves this
purpose already. i originally created the hook for implementing mem
streams based on a mistaken reading of posix, and later realized it
wasn't useful but never removed it until now.
the old behavior was to only consider a stream to be "reading" or
"writing" if it had buffered, unread/unwritten data. this reportedly
differs from the traditional behavior of these functions, which is
essentially to return true as much as possible without creating the
possibility that both __freading and __fwriting could return true.
gnulib expects __fwriting to return true as soon as a file is opened
write-only, and possibly expects other cases that depend on the
traditional behavior. and since these functions exist mostly for
gnulib (does anything else use them??), they should match the expected
behavior to avoid even more ugly hacks and workarounds...
this is required in case dtors use stdio.
also remove the old comments; one was cruft from when the code used to
be using function pointers and conditional calls, and has little
motivation now that we're using weak symbols. the other was just
complaining about having to support dtors even though the cost was
made essentially zero in the non-use case by the way it's done here.
these are not exposed publicly in any header, but the few programs
that use them (modutils/kmod, etc.) are declaring the functions
themselves rather than making the syscalls directly, and it doesn't
really hurt to have them (same as the capset junk).
based on patch by Emil Renner Berthing, with minor changes to dirent.h
for LFS64 and organization of declarations
this code should work unmodified once a real strverscmp is added, but
I've been hesitant to add it because the GNU strverscmp behavior is
harmful in a lot of cases (for instance if you have numeric filenames
in hex). at some point I plan on trying to design a variant of the
algorithm that behaves better on a mix of filename styles.
these were left in glibc for binary compatibility after the public
part of the interface was removed, and libcap kept using them (with
its own copy of the header files) rather than just making the syscalls
directly. might as well add them since they're so small...
i originally omitted these (optional, per POSIX) interfaces because i
considered them backwards implementation details. however, someone
later brought to my attention a fairly legitimate use case: allocating
thread stacks in memory that's setup for sharing and/or fast transfer
between CPU and GPU so that the thread can move data to a GPU directly
from automatic-storage buffers without having to go through additional
buffer copies.
perhaps there are other situations in which these interfaces are
useful too.
printf was not printing too many characters, but it was reading one
too many wchar_t elements from the input. this could lead to crashes
if running off the page, or spurious failure if the conversion of the
extra wchar_t resulted in EILSEQ.
the error will propagate up and be printed to the user at program
start time; at runtime, dlopen will just fail and leave a message for
dlerror.
previously, if mprotect failed, subsequent attempts to perform
relocations would crash the program. this was resulting in an
increasing number of false bug reports on grsec systems where rwx
permission is not possible in cases where users were wrongly
attempting to use non-PIC code in shared libraries. supporting that
usage is in theory possible, but the x86_64 toolchain does not even
support textrels, and the cost of keeping around the necessary
information to handle textrels without rwx permissions is
disproportionate to the benefit (which is essentially just supporting
broken library setups on grsec machines).
also, i unified the error-out code in map_library now that there are 3
places from which munmap might have to be called.
Per POSIX, "The abort() function shall cause abnormal process
termination to occur, unless the signal SIGABRT is being caught and
the signal handler does not return."
If SIGABRT is blocked or if a signal handler is installed and does
return, abort is still required to cause abnormal program termination.
We cannot use a_crash() to do this, since a SIGILL handler could also
be installed (and might even longjmp out of the abort, not expecting
to be invoked from within abort), nor can we rely on resetting the
signal handler and re-raising the signal (this has race conditions in
multi-threaded programs). On the other hand, SIGKILL is a perfectly
safe, unblockable way to obtain abnormal program termination, and it
requires no ugly loop-and-retry logic.
for some nonsensical reason, glibc's headers use inline functions that
redirect some of the standard functions to ugly nonstandard names (and
likewise for some of their nonstandard functions).
I've been looking for data that would suggest a good default, and
since little has shown up, i'm doing this based on the limited data I
have. the value 80k is chosen to accommodate 64k of application data
(which happens to be the size of the buffer in git that made it crash
without a patch to call pthread_attr_setstacksize) plus the max stack
usage of most libc functions (with a few exceptions like crypt, which
will be fixed soon to avoid excessive stack usage, and [n]ftw, which
inherently uses a fair bit in recursive directory searching).
if further evidence emerges suggesting that the default should be
larger, I'll consider changing it again, but I'd like to avoid it
getting too large to avoid the issues of large commit charge and rapid
address space exhaustion on 32-bit machines.
this fix is necessary because a program could be started with some of
the implementation-reserved signals masked (e.g. due to exec having
been called from a signal handler, or from a non-musl program) and
then could obtain an invalid-to-use-later sigset_t as the old/saved
signal mask.
this action is now performed in pthread_self initialization; it must
be performed there in case the first call to pthread_create is from a
signal handler, in which case the old signal mask could be restored on
return from the signal.
this should be the last major fix needed to support running
glibc-linked conforming POSIX programs with musl in place of glibc, as
long as musl provides the features they need and they don't use
pthread cancellation (which is implemented as c++ exceptions in glibc,
and fundamentally incompatible with musl).
these will NOT be used when compiling with -D_LARGEFILE64_SOURCE on
musl; instead, they exist in the hopes of eventually being able to run
some glibc-linked apps with musl sitting in place of glibc.
also remove the (apparently incorrect) fcntl alias.
two actual issues: one is that __dynlink no longer wants/needs a GOT
pointer argument, so the code to generate that argument can be
removed. the other issue was that in the i386 code, argc/argv were
being loaded into registers that would be call-clobbered, then copied
to preserved registers, rather than just being loaded into the proper
call-preserved registers to begin with.
this cleanup is in preparation for adding new dynamic linker
functionality (ability to explicitly invoke the dynamic linker to run
a program).
Rich Felker